Growing evidence favors the use of human milk for the feeding of preterm infants based on its many beneficial effects, including on infectious-related outcomes. However, contaminated human milk can act as the vehicle of transmission for a number of infections. Pasteurization inactivates most bacteria and viruses in the milk but likewise affects the immunological and nutritional quality of the milk. As a result of these effects, we hypothesized that short term infection-related benefits of human milk feeding for very low-birth-weight infants are decreased by the process of pasteurization. Furthermore, we aimed to evaluate the impact of type of enteral feeding, comparing raw and pasteurized mother&acute;s own milk and formula milk, on the colonization of the intestinal microbiota, which plays an important role in the protection against invasive infections. Chapter 1, the introduction of this thesis, gives an overview of the benefits of human milk in reduction of infection-related morbidity in preterm infants, the intestinal microflora and its relation to infection, the hazards of microbial contamination and quality control of expressed maternal milk and the effects of pasteurization. Furthermore, the outline and aims of the thesis are described. In chapter 2, we document the diversity in current practices for the use of human milk in neonatal intensive care units in Belgium and Luxembourg, especially regarding storage and processing procedures. In chapter 3, we focus on clinical management issues on the use of expressed mother&acute;s own milk in the neonatal intensive care unit and apply the principles of hazard analysis and critical control points on the handling of expressed mother&acute;s own milk. In chapter 4, the first randomized controlled trial on pasteurization of mother&acute;s own milk for very low-birth-weight infants shows that pasteurization does not significantly reduce the risk of serious infectious morbidity. On the contrary, there is a trend towards a lower incidence of bloodstream infections in infants assigned to receive raw, untreated expressed milk. Intestinal colonization patterns of staphylococci, the most frequent causative microorganism of nosocomial sepsis, is not associated with the type of enteral feeding, as was described in chapter 5. In addition, we found that, in most patients exhibiting a bloodstream infection, intestinal colonization retrieves a predominant strain that is different from the one recovered from the blood. We speculate that, in case of staphyolococcal invasive infection, an endogenous portal of entry plays a minor role. The in vitro effects of Holder pasteurization on the immunological quality of maternal milk are further described in chapter 6. In chapter 6a, we found a low mannose binding lectin activity in human milk, without difference between pasteurized and non-pasteurized milk. On the other hand, pasteurization significantly reduces the soluble CD14 concentration in expressed human milk. In chapter 6b, we focused on the effect of pasteurization on the antibacterial properties of human milk. In milk samples inoculated with Staphylococcus aureus or Escherichia coli, growth inhibition is significantly lower in the pasteurized milk compared to raw milk. The results of this thesis suggest that pasteurization of mother&acute;s own milk is not an effective strategy to minimise the risk of serious infectious morbidity; minimizing exogenous bacterial contamination of expressed milk, using the HACCP approach, has priority.